1. Field of The Invention
The present invention generally relates to an electromagnetic clutch, such as for use in controlling the transmission of power from an automobile engine to a refrigerant compressor in an automotive air conditioning system, and, more particularly, to an electromagnetic clutch having a structure for reducing impact noise when an armature plate is attracted to a rotor.
2. Description of The Prior Art
Generally, there are two types of well-known electromagnetic clutches which include a structure to transfer rotational and attractive forces: one type includes a plurality of leaf springs to transfer the forces and the other type includes a plurality of rubber members to transfer the forces. For example, U.S. Pat. No. 4,694,945 discloses a plurality of leaf springs which transfer rotational force from a clutch rotor to an armature plate as the armature plate engages the clutch plate of the clutch rotor. Issued Japanese Utility Model No. 58-8997 discloses a plurality of rubber members which transfer rotational force from the clutch rotor to the armature plate as the armature plate engages the clutch plate of the clutch rotor.
In systems such as that described in above-mentioned U.S. Pat. No. 4,694,945, when the electromagnet associated with the clutch is excited, the armature plate is attracted to one end surface of a rotor against the recoil strength of the leaf springs. As the axial air gap between the armature plate and the rotor is made smaller, the attractive force attracting the armature plate to the rotor increases. Accordingly, the kinetic energy of the armature plate is large just before the armature plate contacts the clutch plate. This kinetic energy of the armature plate is converted to sound energy and vibration as the armature plate contacts the clutch plate. Therefore, when the armature plate is attracted to the rotor, large impact noise and vibration is produced between the armature plate and the rotor. Systems such as that described in the above-mentioned Issued Japanese Utility Model No. 58-8997 reduce this noise and vibration by the use of rubber members. However, the effectiveness and durability of these rubber members is decreased by the rotational stress applied thereto immediately after the armature plate engages the clutch plate.
U.S. Pat. No. 4,808,870 discloses an improved connecting structure between an armature plate and a stopper plate for reducing impact noise when the armature plate is attracted to a rotor. This structure is an improvement over the above-described systems in that impact noise is reduced and the durability of the elastic members is increased. However, in this system, the connecting structure includes an elastic member fixedly secured to an associated pin member. While the elastic member is not subject to rotational force, the absorption of impact noise is accomplished by the elastic member receiving shearing stress produced by the axial movement of the pin member. This shearing stress has a detrimental effect on the durability of the elastic member.